1. Field of the Invention
The present invention relates to the preparation of polymers or copolymers based on methyl methacrylate (MMA) which are modified by imidation, via reaction with an amine, of the ester functional groups comprising same, to improve various properties thereof.
This invention also relates to such imidation-modified polymers or copolymers based on MMA, per se.
2. Description of the Prior Art
It is known to this art to produce polymers based on MMA via imidation using an amine, for example by imidation:
(a) of molten polymer in an extruder, PA1 (b) of polymer dissolved in a solvent, and PA1 (c) of polymer in suspension in aqueous phase.
These processes present a number of disadvantages. Thus, the aforenoted processes for imidation in molten state present the disadvantage of poor control and heterogeneity of the imidation, by reason of a reaction between the highly viscous molten polymer and a gas (for example methylamine), a reaction which must be carried out in a very short time (3 to 5 min residence time in the extruder). They also present the disadvantage of heterogeneity of temperature within the molten polymer.
Homogeneous phase processes in a solvent medium present the disadvantage of requiring a costly devolatilization and, in addition, of producing polymers or copolymers containing higher proportions of carboxylic or anhydride functional groups.
Aqueous suspension processes present the disadvantage that the reaction proceeds through a stage of dissolution of the beads or pearls as a result of the formation of carboxylic functional groups, effecting a large increase in viscosity; the polymer reprecipitates only incompletely at the end of reaction. They also present the disadvantage of giving rise to high residual acid and amide contents and therefore producing a modified polymer or copolymer exhibiting poor optical and aging properties.